Winding core and magnetic recording medium producing method

ABSTRACT

A winding core  10  according to the present invention has a cylindrical outer peripheral surface and arranged in a manner that when a web is wound around the outer peripheral surface and so a predetermined pressure acts on the outer peripheral surface, the deformation distortion γ(=ΔR/R) of the outer peripheral surface along the radial direction thereof is equal to or less than 0.001. In this case, ΔR represents the maximum deformation amount along the radial direction of the outer peripheral surface of the winding core and R the diameter of the outer peripheral surface of the winding core upon no occurrence of deformation.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a winding core and a magneticrecording medium producing method and, more particularly, relates to awinding core and a magnetic recording medium producing method which canreduce the probability of the occurrence of the failure of a web in theproducing process etc. of the magnetic recording medium.

[0003] 2. Description of the Related Art

[0004] The producing process of a magnetic recording medium includes aprocess of setting a winding core (supply roller) around which a longbelt-shaped supporting member is wound to a coating apparatus, a processof coating magnetic material or non-magnetic material on one surface ofthe supporting member while feeding the supporting member from thewinding core, and a process of winding the supporting member having beencoated around a winding core (take-up roller), etc. The supportingmember thus wound around the supply roller is formed by polyethyleneterephthalate (PET) etc.

[0005]FIG. 4 shows a conventional example of a winding core used as asupply roller or a take-up roller. The winding core 80 includes acylindrical portion 81 having a cylindrical outer peripheral surface. Anannular pivoting member 83 is fitted in and screwed to the both endportions of the cylindrical portion 81. A web (including a supportingmember being not coated thereon or a supporting member subjected to acoating process or other predetermined processing, etc. in thespecification) W as a long belt-shaped supporting member is wound aroundthe winding core 80. There is a case that the web with the length of9000 to 10000 m is wound around the winding core 80.

[0006] However, since the thickness of the magnetic recording medium hasbecome thinner in order to cope with the tendency of the high density ofthe magnetic recording medium, the following new problem arises. Thatis, as shown by an enlarged view in FIG. 4, when the web W is woundaround the winding core 80 to increase the laminated wound number aroundthe cylindrical portion 81, there arises a case that the web W woundnear the outer peripheral surface of the cylindrical portion 81. Inother words, the web W at the lower layer is bent at some portions anddeformed as if it is buckled. To be more concrete, the web W is deformedin a manner that projections protruding in the outer diameter directionor not-shown projections protruding in the inner diameter direction fromthe plane in parallel to the outer peripheral surface of the cylindricalportion 81 are formed at some portions on the web W along the axialdirection of the cylindrical portion 81. Such deformation occurs notonly at the web W of the lowest layer but also the web W over plurallayers. For example, there arises a case that such deformation occursover the range of about 5% of the entire distance H of the winding core80, around which winding operation of the web W has been completed, fromthe outer peripheral surface of the cylindrical portion 81 to the mostouter peripheral surface of the web W.

[0007] Since the failure portion at which such deformation occurred mustbe disposed, the productivity of the magnetic recording media isdegraded.

SUMMARY OF THE INVENTION

[0008] The invention has been made in view of the aforesaid problem ofthe conventional art, and an object of the invention is to provide awinding core which does not cause the deformation failure of a web evenwhen the thin web is wound around the winding core to increase thelaminated wound number thereof and to provide a magnetic recordingmedium producing method which does not cause the deformation failure ofthe web around the winding core.

[0009] The inventors of the invention have found that when the web W iswound around the winding core 80 to increase the laminated wound numberthereof, there is a case that the outer peripheral surface of thecylindrical portion 81 deforms in the inner diameter direction of thecylindrical portion, which becomes a cause for raising the deformationof the web W. That is, the cylindrical portion is deformed by thewinding fastening force of the web W in a manner that the diameter ofthe outer peripheral surface of the cylindrical portion 81 of thewinding core 80, in particular, the diameter of the outer peripheralsurface at the center portion along the axial direction of thecylindrical portion 81 becomes smaller as compared with thenon-deformation case.

[0010] Then, the inventors investigated wholeheartedly the aforesaidfact and have thought the following configurations 1 to 4.

[0011] Configuration 1: A winding core comprising a cylindrical outerperipheral surface and, when a web is wound around the outer peripheralsurface and so a pressure of 300 Pa acts on the outer peripheralsurface, deformation distortion γ along a radial direction of the outerperipheral surface, represented by a following expression [1], is equalto or less than 0.001

γ=ΔR/R  [1]

[0012] where, in the expression [1], AR represents a maximum deformationamount along the radial direction of the outer peripheral surface of thewinding core and R represents a diameter of the outer peripheral surfaceof the winding core upon no occurrence of deformation.

[0013] Configuration 2: In a method of producing a magnetic recordingmedium including a process of winding a web around a winding core, theweb is wound around the winding core so that a following expression [2]is satisfied when the web is wound around an outer peripheral surface ofthe winding core and so a pressure of 300 Pa acts on the outerperipheral surface

ΔR/R≦0.001  [2]

[0014] where, in the expression [2], ΔR represents a maximum deformationamount along a radial direction of the outer peripheral surface of thewinding core and R represents a diameter of the outer peripheral surfaceof the winding core upon no occurrence of deformation.

[0015] Configuration 3: In a winding core having a cylindrical outerperipheral surface, wherein a pressure acts on the outer peripheralsurface when a web is wound around the outer peripheral surface, adeformation coefficient β of the winding core, represented by afollowing expression [3], is equal to or less than 6.0×10⁻¹¹

β=ΔR×P/R ²  [3]

[0016] where, in the expression [3], ΔR represents a maximum deformationamount (m) along a radial direction of the outer peripheral surface ofthe winding core, P represents a pressure (N/m²) acting on the outerperipheral surface of the winding core and R represents a diameter (m)of the outer peripheral surface of the winding core upon no occurrenceof deformation.

[0017] Configuration 4: In a method of producing a magnetic recordingmedium including a process of winding a web around a winding core, theweb is wound around the winding core so that a following expression [4]is satisfied

ΔR×P/R ²≦6.0×10⁻¹¹  [4]

[0018] where, in the expression [4], ΔR represents a maximum deformationamount (m) along a radial direction of an outer peripheral surface ofthe winding core, P represents a pressure (N/m²) acting on the outerperipheral surface of the winding core and R represents a diameter (m)of the outer peripheral surface of the winding core upon no occurrenceof deformation.

[0019] According to the winding core of the configurations 1 and 3, evenwhen the long web is wound around the winding core and so a largepressure due to the winding fastening force of the web acts on the outerperipheral surface of the winding core, the winding core scarcelydeforms in the radial inner direction thereof. Thus, the deformationfailure of the web scarcely occurs and so an amount of the web whichmust be disposed can be reduced remarkably.

[0020] Incidentally, in the configurations 1 and 3, although the meansfor satisfying the expression [1] and/or the expression [3] is notlimited, as such means, the invention may provide a reinforcement memberfor improving the rigidity of the winding core in the radial directionthereof, a solid-core portion in the winding core, the processing on thesurface of the winding core for improving the rigidity thereof, etc.

[0021] According to the producing method of a magnetic recording mediumof the configurations 2 and 4, the deformation failure of the webscarcely occurs and so an amount of the web which must be disposed canbe reduced remarkably. Thus, the productivity of the magnetic recordingmedium can be improved.

[0022] Incidentally, in the configurations 2 and 4, various methods maybe employed in order to wind the web around the winding core so as tosatisfy the expression [2] and/or the expression [4]. For example, it isconsidered that the winding core described in the configurations 1 and 3may be employed as a supply portion and a take-up portion.Alternatively, it is considered to control the tension of the web.

[0023] The gist of the configurations 2 and 4 resides in that theentirety of the winding core is thought as if it is an elastic memberhaving elasticity along the radial direction thereof, then thedeformation coefficient β which is different from the elasticcoefficient but similar thereto is defined and the deformationcoefficient is set to be equal to or less than a predetermined value.

BRIEF DESCRIPTION OF THE DRAWINGS

[0024]FIG. 1A and 1B are partially cut-away views showing an embodimentof the present invention;

[0025]FIG. 2 is a schematic diagram showing an apparatus for executingthe invention;

[0026]FIG. 3 is a graph showing the relation between deformationcoefficients and failure occurrence probabilities in an example and acomparative example, and

[0027]FIG. 4 is a partially cut-away view showing a conventional windingcore.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0028] The embodiment of the invention will be explained based on theaccompanying drawings. FIG. 1A and 1B show a winding core 10 accordingto the embodiment of the invention. As shown in FIG. 1A, the windingcore 10 is configured in a manner that an annular supporting portion 12is fitted at the both ends of the cylindrical portion 11 thereof. Thesupporting portion 12 has a small-diameter cylindrical portion 12 awhich protrudes from the both ends of the cylindrical portion 11 and hasa diameter smaller than that of the cylindrical portion 11. A pivotingmember 13 is fitted and fixed by a screw etc. to the projection end ofthe small-diameter cylindrical portion 12 a.

[0029] An inner peripheral surface supporting member 15 serving as areinforcement member for improving the rigidity of the winding core 10in the diameter direction thereof is fitted at the inner peripheralsurface at the center portion along the axial direction of thecylindrical portion 11.

[0030] As shown in FIG. 1B which is a diagram seen toward an arrow B inFIG. 1A, the inner peripheral surface supporting member 15 is arrangedin a manner that a center hole 17 and lightening portions 18 areprovided at a circular-plate shaped member 16 whose outer peripheralsurface fits against the inner peripheral surface of the cylindricalportion 11.

[0031] Since the winding core 10 shown in FIG. 1 is provided with theinner peripheral surface supporting member 15, the following expressions[1] and [2] are satisfied.

γ=ΔR/R  [1]

ΔR/R≦0.001  [2]

[0032] In the expressions [1] and [2], γ represents the deformationdistortion along the radial direction of the winding core, ΔR representsthe maximum deformation amount along the radial direction of the outerperipheral surface of the winding core and R represents the diameter ofthe outer peripheral surface of the winding core upon no occurrence ofdeformation.

[0033] According to the winding core 10 thus configured, even when thelong web is wound around the winding core and so a large pressure due tothe winding fastening force of the web(for example 300 Pa) acts on theouter peripheral surface of the winding core, the cylindrical portion 11scarcely deforms in the radial inner direction. Thus, the web hardlydeforms.

[0034] The winding core according to the invention is not limited to theaforesaid embodiment and the winding core may be subjected to suitabledeformation, improvement etc.

[0035] For example, as the inner peripheral surface supporting member, amember including a ring member whose outer peripheral surface fitsagainst the inner peripheral surface of the cylindrical portion and aplurality of bridging rods for supporting the ring member etc. may beemployed.

[0036] Further, in order to improve the rigidity in the radial directionof the winding core, the cylindrical portion may be formed by materialwith high rigidity (for example, Young's modulus of 125 GPa) instead ofusing the reinforcement member. Alternatively, a member with a highrigidity may be wound around the cylindrical portion instead of usingthe reinforcement member.

[0037] Young's modulus of bakelite which is an example of the materialof the conventional winding core is 7 GPa.

[0038]FIG. 2 is a diagram showing the configuration of a coatingapparatus for carrying out the producing method of the magneticrecording medium according to the invention. Incidentally, otherapparatus etc. may be employed and applied to the invention.

[0039] The coating apparatus 30 includes a coating section 31 and acalendar section 32. In the coating section 31, the web W is suppliedfrom a supply portion 33 which is formed by winding the web on the outerperipheral surface of the winding core 10 shown in FIG. 1. The web Wthus supplied is transferred by driving rollers 34 such as suitabletransfer rollers, suction drums with grooves etc. and passed through afirst dry zone 36, a back coating portion 37 and a second dry and heatprocessing zone 38.

[0040] Aramid or PET etc. may be employed as the material of thesupporting member (web), but the material of the supporting member isnot limited thereto.

[0041] The web W passed through the coating section 31 is subjected tothe calendar processing by the calendar section 32. That is, the web Wis subjected to the calendar processing in a manner that the web issandwiched and transferred between calendar rollers 40 and 41 andcalendar rollers 41 and 42.

[0042] The web W having passed the calendar section 32 is wound in aroll shape by a take-up portion 43 having the winding core 10 shown inFIG. 1.

[0043] According to the aforesaid producing method of the magneticrecording medium using the coating apparatus 30, since the deformationfailure of the web W hardly occurs at the supply portion 33 and thetake-up portion 43, an amount of the web W which must be disposed can bereduced remarkably. Thus, the productivity of the magnetic recordingmedium can be improved.

Embodiment

[0044] The remarkable effects of the invention will be explained basedon the embodiment of the invention.

[0045] As the winding core of the take-up portion 43 of the coatingapparatus 30 shown in FIG. 2, three winding cores each having theconfiguration shown in FIG. 1 and a deformation coefficient β of1.5×10⁻¹¹ are prepared and three winding cores each having theconfiguration shown in FIG. 1 and a deformation coefficient β of4.5×10⁻¹¹ are prepared. The web of 10000 m is wound around these windingcores and then observation was made as to the deformation failure of theweb. The observation result is shown in the graph of FIG. 3.

[0046] As a comparative example, three winding cores each not having theinner peripheral surface supporting member 15 shown in FIG. 1 but havinga deformation coefficient β of 7.0×10⁻¹¹ are prepared and three windingcores each not having the inner peripheral surface supporting member 15shown in FIG. 1 but having a deformation coefficient β of 1.3×10⁻¹⁰ areprepared. The web of 10000 m is wound around these winding cores andthen observation result of the deformation failure of the web is alsoshown in the graph of FIG. 3.

[0047] In FIG. 3, the failure occurrence probability represents a %range with respect to the entire distance H (see FIG. 4) from the outerperipheral surface of the cylindrical portion to the most outerperipheral surface of the web where the deformation failure of the weboccurred. The diameter of the outer peripheral surface of each of thewinding cores is 300 mm.

[0048] As shown in FIG. 3, when the deformation coefficient β is equalto or less than 2.0×10⁻¹, the failure occurrence probability is almost0. When the deformation coefficient β exceeds 2.0×10⁻¹¹, the failureoccurrence probability increases gradually, and the failure occurrenceprobability becomes 1% when the deformation coefficient is 6.0×10⁻¹¹.Further, when the deformation coefficient β exceeds 6.0×10⁻¹¹, thefailure occurrence probability increases rapidly. For example, when thedeformation coefficient β is 1.3×10⁻¹⁰, the failure occurrenceprobability becomes 5% or more.

[0049] When the failure occurrence probability is 1% or less, an amountof the web which must be disposed can be reduced remarkably and so theproductivity of the magnetic recording medium can be improved.

[0050] As described above, according to the invention, even when thelong web is wound around the winding core and so a large pressure actson the outer peripheral surface of the winding core, the winding corescarcely deforms in the radial inner direction thereof. Thus, thedeformation failure of the web scarcely occurs and so an amount of theweb which must be disposed can be reduced remarkably.

[0051] Therefore, according to the invention, the productivity of themagnetic recording medium can be improved.

What is claimed is:
 1. A winding core comprising a cylindrical outerperipheral surface for winding a web, wherein when a predeterminedpressure acts on said outer peripheral surface by winding web,deformation distortion γ of said outer peripheral surface along radialdirection thereof satisfies following expressions: γ=ΔR/R≦0.001, andγ≦0.001, wherein ΔR represents a maximum deformation amount along saidradial direction of said outer peripheral surface of said winding coreand R represents a diameter of said outer peripheral surface of saidwinding core upon no occurrence of deformation.
 2. A winding corecomprising a cylindrical outer peripheral surface for winding a web,wherein when a pressure acts on said outer peripheral surface by windingsaid web, deformation coefficient β of said winding core satisfiesfollowing expressions: β=ΔR×P/R ² and, β≦6.0×10⁻¹¹, wherein ΔRrepresents a maximum deformation amount (m) along a radial direction ofsaid outer peripheral surface of said winding core, P represents apressure (N/m²) acting on said outer peripheral surface of said windingcore and R represents a diameter (m) of said outer peripheral surface ofsaid winding core upon no occurrence of deformation.
 3. The winding coreaccording to claim 1 , comprising a supporting portion which fits anouter surface thereof fits to an inner surface of said winding core. 4.A method for producing a magnetic recording medium comprising a step ofwinding a web around a winding core, wherein when a predeterminedpressure acts on an outer peripheral surface of said winding core bywinding said web, a following expression is satisfied at said outerperipheral surface: ΔR/R≦0.001, wherein ΔR represents a maximumdeformation amount along a radial direction of said outer peripheralsurface and R represents a diameter of said outer peripheral surface ofsaid winding core upon no occurrence of deformation.
 5. A method forproducing a magnetic recording medium comprising a step of winding a webaround a winding core, wherein a following expression is satisfied at anouter peripheral surface of said winding core: ΔR×P/R ²≦6.0×10⁻¹¹,wherein ΔR represents a maximum deformation amount (m) along a radialdirection of an outer peripheral surface, P represents a pressure (N/m²)acting on said outer peripheral surface of said winding core and Rrepresents a diameter (m) of said outer peripheral surface of saidwinding core upon no occurrence of deformation.